Hydraulic system for braking truck engines

ABSTRACT

An energy absorbing system operable in conjunction with a pump powered off of the vehicle drive train, the system including a driver control panel including a settable relief valve permitting control of remote pilot operated relief valves for variable loading of the pump for vehicle braking purposes. Pump discharge is by-passed around the driver control relief valve during open throttle conditions while conversely a closed throttle position, during deceleration, will automatically close the by-pass to subject pump output to variable loading by the operator controlled relief valve. Additionally, manually operated control valves assure system operation in the event of component failure.

BACKGROUND OF THE INVENTION

The present invention concerns a hydraulic system for selectivelyloading a hydraulic pump to absorb driveline energy of a vehicle tobrake same. The broad concept of utilizing hydraulic pumps and the liketo absorb energy from a vehicle driveline is well known as evidenced byU.S. Pat. No. 3,759,355 granted to the present inventor with otherhydraulic braking systems being disclosed in U.S. Pat. Nos. 2,905,276;3,185,261; and 3,593,828.

The systems disclosed in the earlier patents are not intended for usewith pump means now often included as a standard transmission componentin certain types of heavy duty trucks. Normally such power take-offpumps are in splined engagement with a truck transmission component andare used for powering hydraulic components such as, for example, thehydraulic rams of a truck having a tiltable dump body.

A further disadvantage to known systems is the lack of back up safetyprovisions and limited driver control of the system. Driver control islimited, for the most part, to either an "on" or "off" condition of theenergy absorbing system.

SUMMARY OF THE INVENTION

The present hydraulic braking system includes pilot operated reliefvalve means, the pilot operating pressure of which is subjected todriver control permitting continuous regulation of the system to suitroad conditions.

The present energy absorbing system relies on a source of fluid pressuredriven as a power take-off unit of the vehicle's transmission. In mostinstances, the pressure source may be a pump provided as originalequipment on the vehicle for the purpose of powering hydraulic truckcomponents. Pump discharged fluid is cycled through a normally opensolenoid valve which is closeable upon closing of the throttle. The pumpis accordingly loaded to the set point of a driver regulated reliefvalve which allows partial unloading of the system. Additional valvecomponents and controls of the system are accessible to the driver on apanel adjacent the driver's station to allow manual adjustment ofcertain of the system valves in the event of component or electricalfailure. Pilot operated relief valves are operable to protect the systemfrom excessive pressures. Means are provided to protect the systemagainst fluid shock loads.

BRIEF DESCRIPTION OF THE DRAWING

In the accompanying drawing:

FIG. 1 is a hydraulic schematic of the present system, and

FIG. 2 is a plan view of a typical control panel in the driver'scompartment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With continuing reference to the accompanying drawing wherein appliedreference numerals indicate parts similarly identified in the followingspecification the reference numeral 10 identifies a transmission case ina truck driveline, the transmission being of the type currently found onheavy duty trucks and particularly those types of trucks havinghydraulic powered accessories.

Indicated at 11 is a positive displacement hydraulic pump suitablymounted on the transmission case and driven by a power take-offcomponent integral with the transmission. A pressure or output line 12communicates pump 11 with a pair of relief valves 13 each being pilotoperated and opening at a pre-set pressure occurring in branches12A--12B of conduit 12. A driver adjustable relief valve at 14 is servedby a line 15. Driver settable relief is located within a drivercompartment outlined at A, and permits driver adjustment of same whileunder way as later elaborated upon. A desirable operating range forrelief valve 14 is from 0 through 2,500 PSI. Valve 14 is of the pilotoperated type but hereinafter referred to as a driver settable reliefvalve.

A solenoid actuated valve is indicated at 16 in a by-pass line 18 whichvalve, upon closing, blocks the low pressure circulation of hydraulicfluid through conduit 15 and by-pass 18. A manually actuated valve 19provides a backup shut-off in by-pass 18 in the event of solenoid valvemalfunction. Solenoid valve 16 is in circuit with and automaticallyenergized by means of a throttle operated switch 20 having contacts 21and 22, one of which is in circuit with a source 25, and closeable uponthe throttle being backed off to a closed position. A manual "ON-OFF"switch at 23 provides the driver with additional control over solenoidvalve 16. A system ON-OFF light is indicated at 24. A normally closedvalve at 26 may be manually opened in the event solenoid valve fails ina closed position to permit by-passing of same. An accumulator at 27 ispre-charged to receive fluid and avert fluid shock to conduit 15 uponclosure of by-pass line 18.

In operation, the power take-off component in transmission 10 is drivenduring deceleration by the drive wheels of the vehicle at a speedproportional with the transmission tail shaft. A low pressure flow offluid passes through conduit 12, conduit 15 and by-pass line 18 forreturn to reservoir R. A heat exchanger 28 cools the fluid during returnto the reservoir.

Braking is initiated by automatic closure of solenoid valve 16 resultingfrom closure of an electrical circuit through throttle closed contacts21 and 22 or, alternatively, manually actuated switch 23 whereupon abuildup of fluid pressure occurs in conduit 15 to the set point ofdriver settable relief valve 14. Accumulator 27 cushions against fluidshock occurring in conduit 15. Pressure buildup in line 15 beyond theset point of valve 14 is relieved by fluid being routed through pilotoperated relief valves 13 and line 17 past heat exchanger 28 toreservoir R. Multiple relief valves 13 are shown, however a single valve13 may be utilized depending on valve capacity and system requirements.Back pressue in communicating conduits 12 and 15 will exert a loadingeffect on pump 11 and hence the drive line. During system operation apressure indicator may be monitored by the driver to assure systempressure being kept within safe limits.

While we have shown but one embodiment of the invention it will beapparent to those skilled in the art that the invention may be embodiedstill otherwise without departing from the spirit and scope of theinvention.

Having thus described the invention what is desired to be secured undera Letters Patent is:
 1. An energy absorbing system for a vehicle drivetrain of the type having a power take-off pump associated therewith,said system comprising,a control panel for said system located at thedriver's station, said control panel including a driver settable reliefvalve in fluid communication with said pump, a system pressureindicator, a relief valve by-pass line, a solenoid actuated valve in therelief valve by-pass line operable in a closed position to divert pumpoutput through said relief valve, switch means in circuit with saidsolenoid valve and operable to close said solenoid valve during vehicledeceleration, and pilot operated relief valve means in communicationwith the power take-off pump, said relief valve means having its pilotin fluid communication with said pump and also with the drivercontrolled relief valve whereby upon closure of the by-pass line by saidsolenoid during vehicle deceleration the build up of fluid pressureacting on the pilot may be regulated by adjustment of the driveroperated relief valve which in turn regulates the opening and closing ofthe pilot operated relief valve means to affect loading of the powertake-off pump for energy absorbing purposes.
 2. The energy absorbingsystem as claimed in claim 1 additionally including a normally openvalve and a normally closed valve disposed in parallel in said reliefvalve by-pass line.
 3. The energy absorbing system as claimed in claim 2wherein said switch means is actuated by the vehicle throttle moving toa closed position.
 4. The energy absorbing system as claimed in claim 1wherein said control panel additionally includes a driver actuatedswitch in parallel with said switch means for alternative closing of thecircuit to said solenoid actuated valve.
 5. The energy absorbing systemas claimed in claim 1 additionally including a pre-charged accumulatorin the by-pass line to avoid fluid shock to the system.